Application of Hall Current Sensor in Telecom Rectifier and Server Power Supply

The power factor correction (PFC) circuit and inverter circuit in the telecom rectifier and server power supply unit (PSU) all need to detect the current signal on the high-voltage side to the controller on the low-voltage side, so isolated current sensors are used. There are many ways to implement isolated current detection, such as current transformers (CT), isolation amplifiers, and Hall-effect current sensors. Among them, the Hall-effect current sensor is an ideal choice because of its simplicity, accuracy, small size, and DC detection capability.

The power factor correction (PFC) circuit and inverter circuit in the telecom rectifier and server power supply unit (PSU) all need to detect the current signal on the high-voltage side to the controller on the low-voltage side, so isolated current sensors are used. There are many ways to implement isolated current detection, such as current transformers (CT), isolation amplifiers, and Hall-effect current sensors. Among them, the Hall-effect current sensor is an ideal choice because of its simplicity, accuracy, small size, and DC detection capability.

The current transformer is based on the principle of the transformer to sample the current, and the CT can be used to detect the turn-on current of the MOSFET or IGBT. The fast response speed of CT makes it very suitable for peak current control and overcurrent protection control. However, the CT based on the principle of transformer coupling cannot sense DC or very low frequency currents, which makes it unable to directly detect power frequency AC currents, or loses measurement accuracy due to the indirect method of detecting only the on-current (no off-current). In addition, because the CT needs to use a ferrite core, it is difficult to make it small, and a larger CT will increase the power switch loop, resulting in higher voltage spikes and noise interference.

The Hall-effect current sensor is a more accurate and smaller choice. It can work under DC conditions and can measure the total AC current including turn-on and turn-off with good linearity and accuracy. At the same time, the volume of the Hall-effect current sensor can be packaged as SOIC-8, and the same integrated IC is the same size, making the layout of the PCB easier and helping to achieve higher power density.

Table 1 compares the Hall-effect current sensor and the current transformer.

Hall effect current sensor

Current Transformer

principle

Hall effect (magnetic field measurement)

Transformer (flux coupling)

Measurement capability

DC and AC

Communication only

size

Minimum: SOIC-8 (5 mm x 6 mm x 1.8 mm)

Minimum: EE5 (7.7 mm x 6.9 mm x 5.4 mm)

Precision

High C up to 1%

Low C depends on many factors

application

DC/AC current detection, PFC current control, inverter current control

Peak current control, overcurrent protection

Table 1: Comparison of Hall-effect current sensors and current transformers

When applying a Hall-effect current sensor to a telecom power supply or server PSU, it is necessary to evaluate the current detection range, continuous current withstand capability, response speed (/bandwidth) and voltage isolation level. In some cases, the telecom power supply or server power supply may also need to report the current operating power to the host computer. At this time, a high-precision Hall current sensor (such as TI’s TMCS1100) can help the system achieve a current detection accuracy of ≥1%.

Figure 1 shows the typical application circuit of the Hall-effect current sensor when using 3.3 V and 5 V power supply respectively. Compared with the use of 3.3 V power supply, the use of 5 V power supply can broaden the current detection range of the Hall sensor. Taking TMCS1100A1 as an example, the sensitivity of the Hall sensor is 50 mV/A: If a 3.3V power supply is used, the current detection range is -33 A? + 33 A (bidirectional); when a 5.0V power supply is used, the current detection range can be extended To -50 A? + 50A. In addition, it should be noted in the design that in addition to the current detection range, the continuous current tolerance of the sensor also needs to be considered. When the current tolerance is insufficient, it can be optimized by improving the heat dissipation of the sensor.

Application of Hall Current Sensor in Telecom Rectifier and Server Power Supply

Application of Hall Current Sensor in Telecom Rectifier and Server Power Supply

Figure 1: Common applications of Hall-effect current sensors: Hall-effect current sensors with 3.3 V power supply (a); Hall-effect current sensors with 5 V power supply (b)

In the layout of the circuit board using the Hall effect current sensor, the following factors should be paid attention to:

l Heat dissipation: Try to increase the copper area of ​​the primary current wire to improve the heat dissipation capacity of the Hall current sensor, thereby increasing the maximum average current tolerance of the sensor. In addition, you can also use a thicker copper foil PCB, or place some heat dissipation vias on the primary traces, or place the Hall current sensor and PCB traces in the air duct, which can improve the average current resistance of the Hall current sensor. Ability.

l Primary-side current magnetic field: During layout, try to avoid high-current traces close to the Hall current sensor.

l Isolation requirements: Consider the creepage distance and electrical clearance from the overall system. When the Hall current sensor cannot meet the required PCB creepage distance, you can dig slots on the circuit board to meet the system-level isolation requirements.

In summary, CT is more suitable for peak current control and overcurrent protection in telecom rectifiers and server PSUs, but it is larger and less accurate. The Hall effect current sensor is small in size, high in accuracy, simple and convenient to use, and is more suitable for detecting AC line current. I hope that the usage of Hall current sensor introduced in this article will be helpful to everyone.

The Links:   LMG6911RPBC-E RM100DZ-24 IGBT-PART

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